Patent GB-1224486-A (GB)
Title: Piston and piston rings unit for an internal combustion engine
IPC: F16J9/20
Filed: 1968-02-17
Abstract: 1,224,486. Piston rings. SEALFIRE. 17 Feb., 1968 [17 Feb., 1967; 29 June, 1967; 18 Jan., 1968], No. 7497/68. Heading F2T. A piston and piston ring unit for an I.C- engine comprises a piston having compression and oil control ring grooves and a ring in each groove, wherein an effective seal is provided between at least one radial face of at least one compression ring and the adjacent radial face of its groove by lapping the faces and/or interposing a sealing joint element between the faces, and wherein access is provided to the opposite radial face of such ring for the pressure existing in the clearance between the piston and cylinder to ensure sealing at the first mentioned radial faces. A compression ring, Fig. 2, is preferably coated with chromium or molybdenum and is either rectangular or slightly trapezoidal in cross-section, the desired effective seal being provided between its lower face and the groove by lapping. The lower adjacent faces may be parallel or tapered as shown and the upper surfaces may also be parallel or tapered to provide a gap open to the gas pressure existing in the clearance between the piston and cylinder; in Fig. 11, the groove is recessed in both its upper and lower faces but in Fig. 9 (not shown), the groove is only recessed in its lower face. Alternatively, the compression ring, Fig. 17, may be sealed to the groove at its lower face by an element 1759 of P.T.F.E., copper or copper alloy which may be rectangular or wedge-shaped in cross-section and formed as a split ring or as a continuous ring provided with radial slits so that it may be flexed or deformed for mounting over the piston; the element may also be formed as a coating or layer which is adhereingly attached to the face of the ring or its groove. In Fig. 21a (not shown) a P.T.F.E. coating (2166) is applied to the opposing ends of the cut in the split compression ring. In Fig. 19 (not shown), the element is supported at its outer periphery by a projection (1963) on the piston. To reduce or prevent the oil pumping effect of the compression ring during operation, a sealing ring may be provided in the bottom of the groove, Figs. 22-26 (not shown), the sealing ring being compressed to cause expansion but prevent rotation of the split compression ring; this sealing ring may be provided with flexible lips (Figs. 23-25) or expansion accommodating bubbles (2675b, Fig. 26b). Figs. 22-26 also illustrate compression rings having curved or conical outer surfaces for engaging the cylinder wall. An effective seal may also be provided at the upper adjacent faces of the oil control ring and its groove by lapping, precision machining or interposing a sealing joint element. The oil control ring may be of the cast iron type of rectangular or slightly trapezoidal cross-section or it may be constructed of two rail rings applied against the faces of the groove and the cylinder wall by an expander. The adjacent upper and the lower faces of the oil control ring and its groove may be parallel with each other or angled to provide tapered gaps. In Figs. 7a- 7c (not shown), the faces of the oil rail ring or the groove are illustrated as being lightly knurled or provided with a surface such as to prevent complete fluid tightness at low pressures and in Figs. 10 and 12 (not shown) the groove is recessed. In Fig. 29 (not shown), the piston is provided with longitudinal grooves (2984) between an annular oil collecting groove (2983) adjacent the compression ring groove and a chamfer (2985) leading into the oil control ring groove. In Fig. 28 (not shown) an oil groove (2879) is provided adjacent the oil control ring groove. In Fig. 27, the sealing joint element between the adjacent upper faces of the oil control ring and its groove is retained in a recess 2778 in the groove and in Fig. 20 (not shown) the element is supported at its outer periphery by a projection (2064) on the piston. When the sealing joint element is made of P.T.F.E., this may incorporate fillers of glass, bronze, graphite or molybdenum disulphide.